We propose a population-based study of a random sample of male residents of Lead-ville, Colorado, approximately half of whom are hardrock miners. Our aims are to compare miners and nonminers for prevalence of chronic bronchitis and other respiratory symptoms, measurements of subclinical small airways abnormalities, and measurements of obstructive and restrictive lung disease, controlling for smoking status. Any health abnormalities found for miners will be related to indices of dust exposure. Subjects will be invited to participate, on the basis of randomly-chosen block of residence, by a local outreach worker who will conduct a census of eligible persons, aged 25 through 64 years. An interviewer will record respiratory, smoking and occupational histories with a questionaire. Physiologic evaluation will include single breath nitrogen test (closing capacity, closing volume, and slope of the alveolar plateau); diffusing capacity of the lung; and plethysmographic measurements (total gas volume, airways resistance, total lung capacity, including forced expiratory volume at 1 second, peak expiratory flow rate, flow rates at 25, 50 and 75% of the vital capacity, and maximal mid-expiratory flow rate). Quality assurance for questionnaire and physiological data will be based on retesting a 10% random sample. Work histories from miner subjects will be spot-checked against Climax Molybdenum Company personnel records and used to calculate an index of occupational dust exposure from industrial hygiene measurements for job classifications and work locations. Data analysis will be based, in part, on prediction equations for normal values of pulmonary function tests at 3,100 meters, developed from data for asymptomatic non-smokers. Our long term objectives are 1) to clarify the physiology and health implications of industrial bronchitis for hardrock miners with silica exposure; 2) to assess whether symptom prevalence and pulmonary function abnormalities seem out of proportion for a miner group at high altitude where minute ventilation is increased; and 3) to evaluate the field use of sophisticated pulmonary physiology evaluation, such as plethysmography and single breath nitrogen tests, for occupational epidemiology.